Field of the Invention
It is the object of the present invention to provide a process for manufacturing succinic acid as obtained by fermentation, said process exhibiting a high yield in terms of succinic acid crystals recovery and allowing to achieve a final product with a low content of saccharides.
Description of Related Art
Succinic acid is a C4-dicarboxylic acid and is an intermediate of the tricarboxylic acid cycle (TCA). Global production of succinic acid is estimated at 16,000 to 30,000 tonnes a year, with an annual growth rate of 10%. Succinic acid finds numerous applications in the cosmetic, pharmaceutical, food industry and in the preparation of polymers. In the food and beverage industry, it is used as an acid regulator or pH controlling agent. In nutraceutical form as a food additive and dietary supplements, succinic acid is safe and approved by the U.S. Food and Drug Administration (FDA). As an excipient in pharmaceutical products it is used to control acidity and, more rarely, in effervescent tablets.
Succinic acid and its derivative diamines and diols can be used as monomer units of a variety of plastics, such as polyesters, polyamides, and polyester amides. Among them, poly(butylene succinate) (PBS) and its copolymers are a family of biodegradable polyesters synthesized from succinic acid, butanediol, or other dicarboxylates and alkyldiols. Owing to their excellent thermal processability, balanced mechanical properties, and good biodegradability, they have attracted intense attention from both academia and industry. PBS products can find wide applications as supermarket bags, packaging film, mulch film, and other disposable articles. It must be pointed out that PBS application of succinic acid requires a high degree of purity of said acid.
Thus far, succinic acid is predominantly produced via petrochemical processes including hydrogenation of maleic acid, oxidation of 1,4-butanediol, and carbonylation of ethylene glycol. However, this route is considered involving processes harmful to the environment. The production of succinic acid from renewable feedstocks—via the so-called biological production route via fermentation- has been focused on as an attractive alternative to petrochemical-based processes. This is an avenue to supplant the more energy intensive and more detrimental to the environment methods of deriving such acid from nonrenewable resources.
Methods of manufacturing succinic acid by fermentation involve basically crystallization of succinic acid from a fermentation broth and the further purification/recovery of succinic acid. From an industrial perspective, achieving a maximal yield in terms of succinic acid crystals recovery is of major importance. Several documents are disclosing for years some routes in order to increase said yield.
EP 2 371 802 discloses a process of crystallizing succinic acid, where an aqueous solution comprising succinic acid is treated with an oxidizing agent, said succinic acid being further crystallized. This method is very efficient in order to remove impurities such as fumaric and orotic acids and to reduce coloration in the final succinic acid crystals, without negatively impacting the global yield in terms of succinic acid crystals recovery. In a preferred embodiment, it is claimed that the mother liquor containing residual succinic acid and impurities, and resulting from the step of crystallization, can be recycled to the step of crystallization, thus allowing to increase the yield of succinic acid crystals produced. In a particular embodiment, the ozone treatment is applied on the mother liquor stream before recycling, in order to remove part of impurities and improve crystals quality.
EP 2 504 307 discloses a process for recovering succinic acid in crystal form from a fermentation broth. Said method comprises the steps of a) bringing the fermentation broth to a pH of between 1 and 4, b) crystallizing the succinic acid, c) dissolving the succinic acid crystals at a temperature ranging from 30 to 90° C., d) polishing and recrystallizing the succinic acid. Succinic acid crystals are obtained, comprising a sugar content of 1 to 100 ppm and a nitrogen content of 1 to 80 ppm. Furthermore, the mother liquor from step b) may be recycled to the feed of step b), said recycling step being found advantageous to increase the yield of succinic acid.
WO 2013/088239 discloses a process for removing color bodies from crude succinic acid, comprising distillation of crude succinic acid and collecting the distillate in a water-containing receiver. The color bodies substantially remain in the distillation bottoms and the purified succinic in the water-containing receiver is substantially free of color bodies. A backward loop can be implemented in order to recycle the distillation residue to the ammonia removal distillation step. Distillation with full recycles has essentially no loss of succinic acid and near quantitative recovery of contained succinic acid is possible.
EP 2 508 501 discloses a method for producing dicarboxylic acids such as succinic acid from fermentation derived solutions containing salts of succinic acid. Said method consists in providing fermentation derived diammonium succinate (DAS) containing solution, converting said solution to a solution containing a half-acid, half-salt of succinic acid (MXS) by reactive evaporation, crystallizing said solution by cooling and/or evaporative crystallization, converting MXS to succinic acid by biopolar membrane electrodialysis, anion exchange, cation exchange, or a combination thereof, and crystallizing succinic acid by cooling and/or evaporative crystallization. It is mentioned that succinic acid contained in the crystallization mother liquor may be recycled to the reactive evaporation step.
WO 2013/039647 discloses a process for the preparation of carboxylic acids like succinic acid (SA) from their corresponding biologically-produced ammonium salts (like DAS) and/or amides and/or imides. The process involves reacting the biologically-produced derivatives at high temperature, removing ammonia and water, crystallizing the carboxylic acid obtained and recycling the mother liquor to the reaction system. Near total recycle of crystallization mother liquor to the process is provided, which yields near quantitative conversion of the biologically produced ammonium carboxylates to the carboxylic acids.
EP 2 371 804 discloses a process for making succinic acid from a clarified diammonium succinate-containing fermentation broth comprising distilling the broth under super atmospheric pressure at a temperature ranging from 100 to 300° C., cooling and/or evaporating the bottoms that comprise succinic acid to separate said bottoms into a liquid portion and a solid portion substantially pure in succinic acid; and separating the solid portion from the liquid portion. The mother liquor from the solids separation step can be recycled to the distillation apparatus in order to enhance the recovery of succinic acid.
CN 102942472 discloses a method of extracting succinic acid from microorganism fermentation liquor. Initially, the succinate fermentation liquor is clarified, then acidized, subjected to reduced pressure distillation and to further cooling crystallization under stirring. The filter liquor obtained is concentrated while the residual mother liquor is subjected to cyclic operation, in order to obtain at least high-purity succinic acid crystals.
In view of the prior art, recycling the mother liquor resulting from the step of crystallization appears to be at least a possible embodiment of the general process and at best as an opportunity to increase the yield of said process. However, yield and purity are generally speaking dual concepts. This is emphasized in EP 2 371 802 that addresses the question of how to achieve a compromise between these 2 parameters.
As a matter of fact, purity is also a main issue dealing with the industrial production of succinic acid, especially in the case of production by fermentation. Such a route uses various bacteria: Actinobacillus succinogenes, Mannheimia succiniciproducens and Escherichia coli, as well as fungi such as Aspergillus niger and Saccharomyces cerevisiae. During the microbial fermentation numerous impurities like organic acids, proteins and the like are also produced. One has also to pay a particular attention to saccharides which are present in the raw material: they cannot be often totally consumed by the microorganism and will contaminate the organic acid to be produced. These and other impurities need to be removed upon recovery of succinic acid from the fermentation broth to obtain succinic acid crystals with a sufficiently high purity. As already mentioned, the use of succinic acid as a monomer for the preparation of PBS requires a high degree of purity of said acid.
Many documents have already addressed the problem of saccharide elimination during the production of succinic acid (or of another organic acid) via the fermentation route. U.S. Pat. No. 6,284,904 discloses a method for separating carboxylic acids from saccharide. The method involves removing impurities by allowing the anionic form of the carboxylic acid to bind to an anion exchange column and washing the column. The carboxylic anion is displaced as carboxylic acid by washing the resin with a strong inorganic anion. However, the corresponding operations for adsorption to the resin, recycle, and the like are complex, and the resin degrades by repeated recycle operations.
JP 2011 219409 discloses a method for producing an aliphatic dicarboxylic acid in a high purification degree by removing various materials originated from a biomass resource with the use of an activated carbon having a specific surface area ranging from 1500 to 5000 m2/g. However, this method cannot be regarded as cheap, facing with the cost not only of the activated carbon but also of the non-recyclable consumable apparatus.
At least, EP 1 686 182 discloses a method of purification owing to the use of organic solvents. Said process comprises heating a mixture of organic acid salt and saccharide, contacting the heated mixture with alcohol, and then separating the organic acid salt from the heated saccharide. However, solvents may be harmful for the environment but also for people. At least, much energy must be consumed for solvent removal, and the cost is too excessive for separating small amounts of saccharide as impurities. Said document also points out that recrystallization or washing for obtaining a high purity organic acid decreases the recovery ratio of the organic acid. Meanwhile, recycling the organic acid for improving its recovery ratio has a problem that trace amounts of saccharide accumulate gradually.
In view of that, one has no choice but to note that there is no efficient process at that date for manufacturing succinic acid, preferably from a fermentation broth, in order to improve the yield of succinic acid crystals recovery and in order to simultaneously achieve a low sugar content into the final product.